Electrical switchboards and other forms of circuit breaker enclosures are typically constructed with cubical or enclosure access doors having openings through which the circuit breaker operating handles extend for convenient manual operation by operating personnel without the necessity of opening the access doors. As a safety precaution for operating personnel, it is common practice to equip each switchboard cubical or circuit breaker enclosure with an interlock which functions to prevent or at least discourage opening of the access door unless and until the circuit breaker therein is open, i.e., OFF.
There are occasions however when it would be most advantageous, if not an absolute necessity, from the standpoint of avoiding disruption of electrical service, for maintenance personnel to gain access to the enclosure without first having to open the circuit breaker. As a consequence, these door interlocks must somehow be defeatable. One way of accomplishing this would be to install the interlock in a manner such that it can be completely removed. This is not a particularly attractive recourse in view of the time and effort required of authorized maintenance personnel. Moreover, defeating the door interlock by its complete removal would be a readily apparent recourse to unauthorized personnel bent on access to the enclosure, and thus any facility in doing so would detract from the intended purpose of discouraging unauthorized access while the circuit breaker is closed. Thus, for the interlock to be effective for its intended purpose, defeatablility should be unobvious to uninformed personnel, regardless of whether it is convenient or not.
It is accordingly an object of the present invention to provide a door interlock for effectively discouraging access to an electrical enclosure while the circuit breaker therein is closed, and yet is readily defeatable by informed, authorized personnel.
A further object of the present invention is to provide a door interlock of the above character which is equipped with unobtrusive interlock defeating provision.
Yet another object of the present invention is to provide an interlock of the above character having provisions for simultaneously padlocking the circuit breaker in its open condition and the enclosure door in its closed position.
An additional object is to provide a door interlock of the above character which is simple in construction, economical to manufacture, reliable in service, convenient to operate by operating personnel in its undefeated condition and readily defeatable by informed maintenance personnel.
Other objects of the invention will in part be obvious and in part appear hereinafter.
In accordance with the present invention, there is provided an interlock for controlling the opening of an access door to an electrical enclosure in accordance with the condition of a circuit breaker situated therein. The interlock includes first and second members commonly mounted to the circuit breaker for movements between respective first and second positions. The first member carries control means disposed in operative relation with a circuit breaker pushbutton which is manipulated from an elevated condition to a depressed condition to convert the breaker from its ON to its OFF condition. Moreover, this pushbutton, while in its depressed condition, inhibits conversion of the breaker from its OFF to its ON condition.
More specifically, the first member control means is arranged to abut the pushbutton in its elevated positions to preclude movement of the first member from its first to its second position. Further, with the pushbutton in its depressed condition, the control means clears the pushbutton to permit movement of the first member from its first position to its second position, and, with the first member at second position, the control means engages the pushbutton to sustain its depressed condition. The second member carries catch means which is disposed, with the second member in its first position, to interfere with the opening of the access door and is disposed, with the second member in its second position, to clear the access door so as to permit opening same.
Coupling means are provided to normally intercouple the first and second members for conjunctive movement between their respective first and second positions. Consequently, the access door cannot be opened until the circuit breaker pushbutton is depressed to open the circuit breaker and, at the same time, permit conjunctive movement of the members from their first positions to their second positions. To accommodate those situations when it is desirable to gain access to the enclosure without having to open the circuit breaker, the coupling means is uniquely designed to be readily, but unobtrusively defeatable by informed personnel so as to decouple the first and second members. With the interlock defeated, the second member may be moved to its second position independently of the first member and thus without having to first depress the pushbutton to open the circuit breaker in order to open the access door.
The interlock of the present invention is further equipped to accommodate padlocking of the circuit breaker in its open condition and the access door in its closed condition. To this end, at least the first member is mounted for movement in a first direction from its first position to its second position and in an opposite direction from its first position to a third position. The control means precludes movement of the first member from its position to its second position until the pushbutton is depressed, and, while in this third position, the control means engages the pushbutton to sustain its depressed condition. Moreover, the first member, in its third position, serves as a catch to preclude opening of the access door. The first member is equipped with provision to accept the hasp of a padlock so as to effectively lock the first member thereat.
The invention accordingly comprises the features of construction, combination of elements, and arrangement of parts which will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims.